Form-sintered metal carbide inserts are often attached to the end of a cutting bar or other machine tool to maximize tool cutting speed and efficiency. Such inserts are generally of polygonal configuration to provide multiple, indexable, cutting edges at the sides and corners of the insert. Generally, the top face of the insert extends at substantially a right angle to the surface of the workpiece and is provided with a "chip breaker" in the form of a groove or other structural configuration. Chip breakers are important to the function of the machine tool as well as to personal safety of the machine operator in that if the turning forms long threads or continuous curls as opposed to being broken into chips, such threads or curls may become wound around the workpiece or become entangled in the machine tool creating substantial risk of personal injury and disturbance of the cutting operation. However, chip breaking under varying working conditions, for example, varying feed and cutting depth, requires careful attention to the combination of feed, cutting depth, and chip breaker configuration.
As a chip breaker breaks the chip only within a certain limited range of cutting depth and feed, as defined by the shape and size of the chip breaker, it is necessary to provide inserts having different chip breaker configurations for different cutting depths and feeds.
A special problem is presented with respect to effective chip breaking in finish cutting because both the cutting depth and the feed are relatively small. A conventional chip breaker chosen with regard to suitable shape and size for rough cutting is unacceptable when the workpiece is to be finished. At small cutting depth it is essential to decrease the rake angle in order to break the chip satisfactorily. Stated another way, it is important to have significant chip breaking capability at the nose of the insert since, at small cutting depths and feeds, the chip has to be sharply bent in order to break because of its small cross section. On the other hand, if the chip breaker is dimensioned for small chip thickness and cutting depth, the angles thereof will be too severe for chip breaking at larger chip thickness and cutting depth.
The deformation or initial bend which the turning receives in the course of separation from the workpiece depends not merely upon its thickness but also upon rake angle. A decreasing rake angle means increasing initial bend but results in increasing cutting forces. Increasing the rake angle permits large cutting depths with relatively smaller cutting forces but decreased initial bend of the turning.
Inserts having a chip breaker at the corner or nose thereof as well as a chip breaker groove alongside the cutting edge of the insert of varying depth and/or width, are well known. Specifically, chip breaking inserts having an initial flat cutting surface which is backed up by an arcuate chip breaking section are taught in the patents to Wirfelt Nos. 3,395,434; Stambler 3,885,281; Gehri 3,968,550 and Newcomer 3,381,349. The chip breaker disclosed in each of the aforesaid patents features an initial flat cutting surface which extends at substantially a right angle to the surface of the workpiece which blends into an arcuate chip breaker. The insert may be orientated at a positive or negative rake, if desired.
Another chip breaking configuration is the "V" configuration as taught in the patents to Krugger Nos. 4,288,179; Seidel 4,056,872; Arnold 4,189,265; and Lundgren 3,866,282.
While the inserts taught in each of the aforesaid patents can be utilized in a specific application, a need exists for an improved insert having an efficient chip breaker for finish cuts as well as cuts of greater depth and feed.